Electrochemical method and system for dyeing and highlighting hair

ABSTRACT

A method for electrochemically dyeing, highlighting or tinting hair is provided which includes first applying to the hair an oxidative dye precursor mixture containing a primary intermediate having a standard Redox potential that is less than about 1V. This precursor mixture on the hair in then contacted with an electrode system that has sufficient voltage to electrochemically oxidize the primary intermediate to produce a colored dye through a coupling reaction. A system or kit for carrying out the method is also provided.

BACKGROUND OF INVENTION

The present invention is directed at methods and compositions forcoloring human and animal hair that do not require the use of chemicaloxidants such as peroxides. The method utilizes electrochemicaloxidation of certain organic oxidative dye precursors to generatereactive intermediates that can then participate in coupling reactionsto form colored molecules capable of dying hair. Specifically, themethod comprises applying to the hair an oxidative dye precursor mixturecontaining at least one primary intermediate and then contacting thismixture on the hair with an electrode system providing sufficientvoltage to generate reactive intermediates through oxidation of theprimary intermediate. The invention also relates to systems (or kits)that provide the means to accomplish these steps.

Permanent hair colorants commonly come in two parts: a dye solution anda developer solution. The developer solution is generally comprised ofan oxidizing agent, typically hydrogen peroxide, and an alkalinebuffering agent such as ammonia. In a conventional permanent haircoloring treatment, the dye solution and the developer solution aremixed and then applied to the hair, which is then left for about 25 minto about 45 minutes. The hair is then rinsed with water, treated with apost treatment conditioner, and then rinsed again with water.

The application of a dye solution in combination with an oxidant affordspermanent hair coloring. However, as is well known, the repeated use ofbleaching agents can damage the hair through indiscriminant oxidation.This is especially important for consumers who either have long hair orwho frequently color their hair.

A second problem associated with conventional permanent hair coloringcompositions and kits for use at home is inconvenience. Since permanentdyes are generated before they are applied to hair, there is thepotential for staining the hands, and face during application and use.This requires gloves, and often masking of areas of the face.

The attainment of natural looking highlights, and tints is anotherproblem encountered with conventional dyeing systems. Although manytypes of styling implements have been suggested in the art, it remainsdifficult for the average consumer to approach the aesthetic quality interms of color nuances that have been heretofore only been available ina salon.

An additional problem associated with conventional dying systems is theconvenient “retouching” of the root areas between complete dying as thehair grows. It is often difficult to match the existing color which haschanged to varying degrees and consequently consumers may be forcedre-dye their hair before it is really necessary.

One objective of the present invention is a method of coloring the hair,especially gray hair that truly does not require a chemical oxidant.

Another objective of the invention is a convenient method of coloringhair that is less messy than conventional dyeing processes and that willprovide a wider range of potential shades and tones from a limited setof chemical compositions.

An additional objective of the invention is a method of dyeing the hairthat is capable of more easily generating natural looking highlights aswell as providing a convenient and effective means of retouching theroot area of hair so as to prolong the duration between hair colorings.

A still further objective is to provide a convenient kit that can beused by individual consumers to practice at home the method describedherein.

These and other objectives will become clear from the description of theinvention.

The following patents and publications have been considered:

U.S. Pat. No. 5,472,456 and U.S. Pat. No. 5,569,368, respectivelydescribe a method and system for electrophoretically applyingtherapeutic and cosmetic agents and dyes especially natural colorantsuch as melanin, to the hair.

Japanese Patent No. JP 6315410 A discloses a method of dyeing hair byflowing an electric current in an acidic hair dying agent coated on thehair until the agent is oxidized to color the hair. The preferred dyesare acidic inorganic compounds especially pyrogallol.

U.S. Pat. No. 5,072,746 discloses a hair grooming device for theelectrocution of lice or other pests on the hair.

None of the references cited above teaches a method of applying to thehair an organic oxidative dye precursor mixture comprising a primaryintermediate having a standard oxidation potential between 10 mV and 3V; and subsequently contacting this mixture on the hair with anelectrode system having sufficient voltage to directly form a reactiveintermediate that generates an indo dye.

SUMMARY OF THE INVENTION

The subject invention provides a method for dyeing the hair by applyingto the hair specific dye precursor compositions and then applying ameans for electrochemically oxidizing these precursors to generatecolored dye molecules that are substantive to the hair thus avoiding theuse of chemical oxidants.

More specifically, the method for electrochemically dyeing the haircomprises carrying out the following steps in the order indicated:

-   -   i) applying to the hair an oxidative dye precursor mixture        containing at least one primary intermediate having a standard        Redox potential less than 1 volt,    -   ii) contacting the oxidative dye precursor mixture on the hair        with an electrode system that provides sufficient voltage to        electrochemically oxidize at least one of the primary        intermediates to produce a reactive intermediate that generates        colored dye through a coupling reaction with an oxidative dye        precursor present in the mixture,    -   wherein the reactive intermediate is a quinone monoimine, a        quinone diimine, a substituted quinone mono- a substituted        quinone diimine, an indole imine, a substituted indole imine, or        mixtures thereof.

A second embodiment of the invention is a system or kit that allowsindividual consumers to conveniently practice the disclosedelectrochemical method of coloring the hair.

More specifically, the hair coloring system or kit comprises:

-   -   i) an oxidative dye precursor mixture containing at least one        primary intermediate having a standard oxidation potential        between 10 mV and 3 V,    -   iii) an electrode system that provides sufficient voltage to        electrochemically oxidize at least one of the primary        intermediates to produce a reactive intermediate that generates        colored dye molecules through a coupling reaction with an        oxidative dye precursor present in the mixture,    -   wherein the reactive intermediate is a quinone monoimine, a        quinone diimine, a substituted quinone mono- a substituted        quinone diimine, an indole imine, a substituted indole imine, or        mixtures thereof.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view schematic of an electrode system for theelectrochemical dyeing of hair wherein the electrodes are combined witha comb aligning means and the power supply is a disposable battery.

FIG. 2 is a schematic of an electrode system for the electrochemicaldyeing of hair wherein the electrodes are combined with a brush aligningmeans and the power supply is provided from DC current by means of an ACto DC converter: A—side view; B—bottom view of section through brushhead.

DETAILED DESCRIPTION OF THE INVENTION

As used herein wt % refers to weight % of an ingredient as compared tothe total weight percent of the composition that is being discussed. Forexample, when wt % is used to discuss the amount of an ingredient thatis in the dye precursor mixture, this means weight % as compared to thetotal weight of the dye precursor mixture.

As used herein “inactive” or “substantially inactive” means that theoxidation hair dye precursors are not chemically reacting or are notchemically reacting to a substantial degree, so as to form coupled orpolymerized hair color molecules, or it means that the oxidation hairdye precursors are not chemically reacting in a substantial manner so asto form coupled or polymerized hair color molecules.

Dye precursor mixtures refers generally to those compositions of thepresent invention which comprise oxidative hair dye precursors and aresuitable for use on human hair, e.g., have the appropriate safetyprofile.

Electrochemical oxidation as used herein, refers to the direct oxidationof an oxidative dye, generally a primary intermediate, by an electrontransfer process which occurs at the anode of an electrode systemapplied to the hair, i.e., an electrolysis process. Thus, an electrodeessentially replaces all or part of chemical oxidant as the electronacceptor in the generation of reactive intermediates.

Aligning and distributing means or simply aligning means, refers to themeans or implement employed to align the hair and distribute the dyeprecursor after the dye precursor is applied to the hair.

The present invention relates to methods and compositions for achievingthe permanent coloring of hair which methods include two key stepsperformed in sequence:

-   -   1) contacting the hair with a substantially inactive dye        precursor mixture of at least one oxidative dye precursor having        a standard Redox potential of less than 1 V for a period of        about 1 second to about 60 minutes, followed by,    -   2) applying to the hair an electrode system that provides        sufficient voltage to electrochemically oxidize at least one of        the primary intermediates to produce a reactive intermediate        capable of generating colored indo dye molecules through a        coupling reaction with an oxidative dye precursor present in the        mixture.

The second step of the above method can be combined with a means ofaligning the hair and distributing the precursor mixture to, forexample, increases, the effective surface area of hair that is exposed,and distribute the dye precursors more uniformly.

The compositions and methods of the present invention may be used tocolor different types of hair such as Asian hair and Caucasian hair. Itis particularly well suited to coloring gray hair.

While not wishing to be bound by theory or in any way limiting the scopeof the invention, the following discussion outlines underlyingprinciples that may be useful in understanding the invention and itspreferred embodiments.

As is well known, the first step in the coloring of hair with anoxidative dye involves the generation of a reactive intermediate via anelectron transfer reaction. Electron transfer reactions can be inducedby using oxidizing agents, e.g., potassium ferricyanide, bleaches likehydrogen peroxide, or by applying a potential sufficient to induceoxidation of the compound at the anode. Organic compounds particularlyamines and phenols in general have sufficiently low Redox potentials toallow them to be preferentially oxidized in water by the application ofa low voltage, i.e., lower than the voltage required for electrolyticoxidation of water to oxygen.

In the process of electrochemical coloring, preferably at least 50%,more preferably 75% and most preferable at least 90% of the colored dyemolecules that are formed, are formed electrochemically and not bychemical oxidation from either a bleach or oxygen present in the air orgenerated electrochemically.

In a standard electrochemical redox reaction, oxidation occurs at theanode and reduction at the cathode, e.g.,Reduction: A+e⁻→A⁻; and Oxidation: B→B⁺+e⁻

When the reaction inside an electrochemical cell is driven by anexternal source of current, it is called an electrolytic cell. If dyeprecursors are kept in contact with an electrochemical source, primaryintermediates such as 4-aminophenol (PAP) and 1,4-phenylenediamines(PPD) and their derivatives undergo oxidation. The quinone imineintermediates so formed can readily couple with appropriate “couplermolecule” to generate indo dye without the use of ammonia and peroxide.A reaction scheme describing the mechanism of electrochemical oxidationof PPD and subsequent coupling to 1,3-dihydroxybenzene through a quinoneimine intermediate to form an indo dyes is given below based on thestudies reported by Klymenko O Y, Giovanelli D, Lawrence N S, Rees N V,Jiang L, Jones T G, and Compton R G in Electroanalysis, 15, 94-960(2003) herein incorporated by reference.

Given the above reaction scheme, possible half cell reactions that canoccur at the anode are the two oxidation steps involving PDP, and theoxidation of water to oxygen. At Anode PPD → PPD^(+•) + e⁻ E^(o) = 0.26V PPD^(•) → QDI + e⁻ E^(o) = 0.72 V 4OH⁻ → O₂ (g) + 2H₂O + 4e⁻ E^(o) =0.401 Vwhere E^(o) is the standard Redox potential expressed as a reductionpotential. In this convention, the smaller (less positive) the value ofthe Redox potential, the easier the material is to oxidize.

Of these possible reactions, the first reaction (oxidation of PPD) isfavored over the formation of oxygen since PPD has a lower Redoxpotential. Thus, the formation of oxygen at the anode should not takeplace until the primary intermediate is exhauted.

The standard Redox potentials for PDP and PDP^(•) were taken fromTechniques of Chemistry Vol. 5, Chapter, Techniques of ElectroorganicSynthesis Part II, Weinberg, N. L (Editor)-1974-1982.

When the cathode is an inert electrode and the solution beingelectrolyzed is a simple alkaline aqueous solution of the dyes and inertelectrolyte, the reaction that takes place at the cathode during theinitial stages of the electrolysis will be the formation of hydrogen. AtCathode 2H₂O + 2e⁻ → H₂ (g) + 2OH⁻ E^(o) = −0.83 V

Thus, for the generation of PPD^(+•) at the anode, a potentialdifference of −1.09V (−(0.26)+(−0.83)) would be required at standardstate. This assumes of course that the standard Redox potential of PPDin water under the pH conditions employed is the same as the potentialvalues quoted above (see below). As the reaction proceeds, however, thereduction of PPD^(+•) and especially QDI becomes a more favored processif appreciable amounts are present in the vicinity of the cathode. Thisis the case because these reactions involving the reduction of the dyehave an overall less negative reduction potential than the generation ofhydrogen gas at alkaline pH. This analysis has implications with respectto electrode design that will be discussed further below.

Upon the application of a potential, PPD first undergoes a one-electronloss (oxidation) at the anode to form the radical-cation speciesPPD^(+•). This species then undergoes a proton exchange with the parentPPD to give the neutral radical species PPD^(•). The neutral radicalspecies then undergoes further one-electron transfer to form thedi-imine. If a coupler molecule is present in solution the di-imineundergoes coupling to form the final indo dye molecule. Of course withother types of primary intermediates other types of reactiveintermediates can be formed such as for example, mono-imines, which alsoparticipate in coupling reactions leading to acceptable dye molecules.

Thus, if a hair sample is dipped into a coloring formula containing dyeprecursors and a voltage of about 0.2 to 3V is applied at a pH of7.0-10.0, respective indo dyes are generated depositing color in thehair.

In the absence of a chemical oxidant, a control sample (no voltage)under identical conditions generates very little color demonstratingthat air oxidation is very slow and the observed color formation resultsfrom electrochemical oxidation. The rate of color formation in the dyebath is much faster in presence of the applied potential compared to thecontrol (air oxidation). The application of a low voltageelectrochemical system will provide sufficient energy to overcome theoxidation potential of the primary intermediates, the critical step inan indo dye formation reaction. Once the primary intermediate isoxidized, subsequent coupling reaction of the QDI with the coupler isvery fast and does not require an oxidant.

It should be understood that the above discussion is meant to illustratethe broad principle of the method with but one, albeit preferred,primary intermediate. Obviously there are other chemical species oforganic primary intermediates that generate different reactiveintermediates and can be used by one skilled in the art and are withinthe broad scope of the invention and the above discussion is not meantto limit the choice.

It will also be understood by those skilled in the art thatconcentrations of oxidative hair dye precursors which may be employed inthe present invention can be varied depending upon, for example, thehair type which is to be colored and on the coloring effect which isdesired.

What follows is a description of the ingredients that can be included inthe mixtures and the electrode system providing the means for carryingout the steps of the present invention.

Dye Precursor Mixture

The dye precursor mixture of the present invention includes oxidativehair coloring precursors (called oxidative or oxidation dyes). Suchoxidative hair coloring agents are used in combination with an electrodesystems of the present invention to deliver color to the hair.

The dye precursor mixture also can contain ingredients used to enhancethe solubility of the precursors in a predominantly aqueous medium(“solubility enhancers”). The mixture can also contain agents to controlthe pH so as to provide an optimal chemical environment for theprecursors to interact with hair fibers (“pH control agents”).

Oxidative Dyes

Permanent hair dye compositions as defined herein are compositions,which once applied to the hair, are substantially resistant to washoutand abrasion.

The dye forming intermediates used in oxidative dyes can be aromaticdiamines, naphthols, aminophenols and their derivatives. These dyeforming intermediates can be classified as; primary intermediates, andcouplers (often also referred to as either secondary intermediates ormodifiers). As used herein the term “precursor” means precursor,coupler, modifier, or intermediate and the like. Primary intermediatesare chemical compounds, which by themselves will form a dye uponoxidation. The coupler or secondary intermediate is used with otherintermediates for specific color effects or to stabilize the color.

At least two types of oxidative dyes can be used in the invention: onetype is a primary intermediate while the other type is a coupler.

Primary intermediates which are suitable for use in the compositions andprocesses herein include aromatic diamines, naphthols, polyhydricphenols, aminophenols and derivatives of these aromatic compounds (e.g.,N-substituted and/or C-substituted derivatives of the amines,O-substituted and/or C-substituted derivatives of phenols).

Primary oxidation dye intermediates are generally colorless moleculesprior to oxidation. Color is generated when the primary intermediate is‘activated’ to form reactive intermediates that subsequently join with acoupler, which is also generally colorless, to form a colored,conjugated molecule. In general terms, oxidation hair dye precursors orintermediates include those monomeric materials which, on oxidation,form oligomers or polymers having extended conjugation systems ofelectrons in their molecular structure.

Because of the new electronic structure, the resultant oligomers andpolymers exhibit a shift in their electronic spectra to the visiblerange and appear colored. For example, oxidation dye precursors capableof forming colored polymers include materials such asp-phenylenediamine, which has two functional groups, and are capable ofoxidative polymerization to yield higher molecular weight coloredmaterials having extended conjugated electron systems.

Preferred primary intermediates have a standard Redox potential lessthat 1V, preferably less than 0.6V and most preferably less than 0.4V.The standards oxidation potentials can be measured by the methodsreported in Techniques of Chemistry Vol 5, Chapter, Techniques ofElectroorganic Synthesis Part II, Weinberg, N. L (Editor)-1974-1982,

A partial list of standard oxidation potentials of several commonoxidative dyes that have been reported in the literature is given inTable 1 below. However, these reported Redox potentials were measured inacetonitrile using a platinum electrode and provide only an estimate ofthe actual oxidation potentials of dyes in an aqueous solution at analkaline pH. The Redox potentials of several useful primaryintermediates measured in aqueous solutions at pH 10 are recorded inTable 1B. It is seen that the standard Redox potentials measured underconditions more representitive to their actual use as hair dyes aresignificantly lower (less positive) than the Redox potentials measuredin the organic solvent acetonitrile. Thus, these primary intermediatesoxidize more readily in water than in an organic solvent as would beexpected.

It is also preferable that the primary intermediates and couplers have apKa in the range from about 3 to about 10, preferably between about 5and about 10. The term pKa has it usual chemical definition: thenegative logarithm of the acid dissociation constant, i.e.,pK_(a)=−log₁₀ K_(a). Thus, a pKa of 5 corresponds to an aciddissociation constant of 10⁻⁵. TABLE 1A Standard Redox Potentials of DyePrecursors in Acylonitrile^(a) Dye Precursors E₁ ^(o), mV E₂ ^(o), mV1,4-Phenylenediamine(PPD) 260 730 2,4-Diaminotoluene (TDA) 7104-Aminophenol (PAP) 120 3-Methyl-4-Aminophenol ˜120 1,3-Phenylenediamine 850 2-Methyl-4-Aminophenol (PAOC) 750 1,3-Dihydroxybenzene 1,1001-Naphthol 1760 N,N-dimethyl PPD 0.25 1.03 Diphenylamine 0.86

TABLE 1B Oxidation Potentials of Primary Intermediates in aqueoussolution at pH 10^(a,b) Primary Intermediates E^(o), mVp-Phenylenediamine (PPD) 99.6 p-Aminophenol (PAP) 67.93-Methyl-4-aminophenol(3M4AP) 70.6 N,N-Bis-hydroxyethyl p- 64.4phenylenediamine p-Toluenediamine 51.9Notes to Table 1^(a)Redox potentials are expressed as reduction potential (i.e., thestandard potential measured for the reduction of the reactiveintermediate to the dye precursor)^(b)The standard Redox potential for PDP is the total or combinedreduction potential for the QDI → PDP.

In one embodiment of the invention, the pH of the dye precursor mixtureis adjusted such that less than 50%, preferably less than 25% and mostpreferably less than 10% of the molecules comprising the dye precursors,i.e., the primary intermediate and coupler, are in their anionic formwhen in contact with the hair during the time period before theelectrical potential is applied to induce oxidation. For example, if theprecursor contains both an amine and an alcohol group, the pH should bebelow the pKa of the hydroxyl group of the alcohol. It has been foundthat this pH environment leads to retention of dye precursor within thehair fiber and color resistance.

In another embodiment of the invention, the pH of the dye precursormixture is adjusted such that more than 50%, preferably more than 75%and most preferably more than 90%, of the molecules comprising the dyeprecursors, i.e., the primary intermediate and coupler, are in theirneutral forms when in contact with the hair during the time periodbefore the electrical potential is applied. For example, if theprecursor is an amine, the pH should be above the pKa of the conjugateacid of the amine precursor, e.g., an ammonium group. If the precursorcontains both an amine and an alcohol group, the pH should be above thepKa of the conjugate acid of the amine but below the pKa of the hydroxylgroup. It has been found that this pH environment can lead to higherretention of dye precursor within the fiber and better color resistance.

Couplers, such as those detailed hereinafter, are preferably used inconjunction with the oxidation dye precursors herein and are thought tointerpose themselves in the colored polymers during their formation andto cause shifts in the electronic absorption spectra thereof, therebyresulting in color changes. A representative list of oxidation dyeprecursors (primary intermediates and couplers) suitable for use hereinis found in Sagarin, “Cosmetic Science and Technology”, Interscience,Special Edition, Volume 2, pages 308 to 310 which is hereby incorporatedby reference.

The typical aromatic diamines, polyhydric phenols, aminophenols, andderivatives thereof, described above as primary dye precursors can alsohave additional substituents on the aromatic ring, e.g. halogen, alkyl,alkyl substituted additional substituents on the amino nitrogen, on thephenolic oxygen, or on the aromatic carbon, e.g., substituted andunsubstituted alkyl and aryl groups.

The hair coloring compositions of the present invention may, in additionto the essential oxidative hair-coloring agents, optionally includenon-oxidative and other dye materials. Optional non-oxidative and otherdyes suitable for use in the hair coloring compositions and processesaccording to the present invention include semi-permanent, temporary andother dyes. Non-oxidative dyes as defined herein include the so-called‘direct action dyes’, metallic dyes, metal chelate dyes, fiber reactivedyes. Numerous examples of these and other synthetic and naturalmaterials can be found in the compendium “Chemical and PhysicalBehaviour of Human Hair” 3rd Edn. by Clarence Robbins (pp 250-259); ‘TheChemistry and Manufacture of Cosmetics’. Volume IV. 2nd Ed. Maison G. Dedyes. Various types of non-oxidative dyes are detailed in: ‘Navarre atchapter 45 by G. S. Kass (pp 841-920); ‘Cosmetics: Science andTechnology’ 2nd Edn, Vol. II Balsam Sagarin, Chapter 23 by F. E. Wall(pp 279-343); ‘The Science of Hair Care’ edited by C. Zviak, Chapter 7(pp 235-261) and ‘Hair Dyes’, J. C. Johnson, Noyes Data Corp., ParkRidge, U.S.A. (1973), (pp 3-91 and 113-139). The above articles arehereby incorporated by reference.

Specific hair dyes which may be included in the compositions as theprimary intermediate includes: 3-methyl-p-aminophenol;2,3-dimethyl-p-aminophenol; p-phenylene diamine, p-toluenediamine;2-chloro-p-phenylenediamine; N-phenyl-p-phenylenediamine;N-2-methoxyethyl-p-phenylenediamine;N,N-bis-(hydroxyethyl)-p-phenylenediamine; 2hydroxymethyl-p-phenylenediamine; 2-hydroxyethyl-p-phenylenediamine;4,4′-diaminodiphenylamine; 2,6-dimethyl-p-phenylenediamine;2-isopropyl-p-phenylenediamine; N-(2-hydroxypropyl)-p-phenylenediamine;2-propyl-p-phenylenediamine;1,3-di-(p-N,N-bis-(2-hydroxyethyl)-aminoanilino)-2-propanol;2-methyl-4-dimethylaminoaniline; p-aminophenol; p-methylaminophenol;2-hydroxymethyl-p-aminophenol; 2-methyl-p-aminophenol;2-(2-hydroxyethylaminomethyl)-p-aminophenol;2-methoxymethyl-p-aminophenol; and 5-aminosalicylic acid; catechol;pyrogallol; o-aminophenol; 2, 4-diaminophenol; 2,4,5-trihydroxytoluene;1,2,4-trihydroxybenzene; 2-ethylamino-p-cresol;2,3-dihydroxynaphthalene; 5-methyl-o-aminophenol;6-methyl-o-aminophenol; and 2-amino-5-acetaminophenol;2,5-diaminotoluene; 2-dimethylamino-5-aminopyridine;-tetra-aminopyrimidine; 4,5-diamino-1-methylpyrazole;4,5-diamino-1-hydroxyethyl pyrazole, 6-methoxy-8-aminoquinoline;2,6-dihydroxy-4-methylpyridine; 5-hydroxy-1,4-benzodioxane;3,4-methylenedioxyphenol; 4-hydroxyethylamino-1,2-methylenedioxybenzene;5-chloro-2,3-dihydroxypyridine;2-hydroxyethylamino-6-methoxy-3-aminopyridine;3,4-methylenedioxyaniline; 5,6-dihydroxyindole; 7-hydroxyindole;5-hydroxyindole; 2-bromo-4,5-methylenedioxyphenol;3-amino-2-methylamino-6-methoxypyridine; 2-amino-3-hydroxypyridine;4-hydroxy-2,5,6-triaminopyrimidine, 5-hydroxyindole, 7 hydroxyindole, 5hydroxyindoline; 7 hydroxyindoline or combinations thereof.

Preferred primary intermediates for use in the invention include:p-phenylenediamine; p-aminophenol;N,N-bis(2-hydroxyethyl)-p-phenylenediamine; 2,5-toluenediamine;2-methyl-p-aminophenol; 3-methyl-p-aminophenol;2,3-dimethyl-p-aminophenol,p-methylaminophenol;4,5,-diamino-1-hydroxyethyl pyrazole, 2,4,5,6-tetrasaminopyrimidine;4-hydroxy-2,5,6-triaminopyrimidine; and mixtures thereof.

The most preferred primary intermediates are those that generate quinonemonoimine, substituted quinone monoimines, quinone dimine, substitutedquinone diimine, indole imine, and substituted indole imine reactiveintermediates resulting from oxidation by the electrode system. Theseespecially preferred primary intermediates include p-phenylenediamine;p-aminophenol; 3-methyl-p-aminophenol;N,N-bis(hydroxyethyl)-p-phenylenediamine; 2,5,-toluenediamine; indolesand substituted indoles such as hydroxyindoles and mixtures thereof.

The primary intermediate is generally present in the precursor mixtureat a level from about 0.005 wt % to about 10 wt %, preferably from about0.01 to about 5 wt %, and most preferably from about 0.01 to about 4 wt%.

The coupler (or secondary intermediate) is utilized to expand the colorrange by reacting with the primary intermediate. These couplers work inconcert with a primary intermediate, which must be present in theprecursor mixture.

Specific hair dye intermediates that can be used as couplers in thepresent invention include: m-aminophenol; 2-methyl-1-naphthol;1-acetoxy-2-methylnaphthalene; resorcinol; 4-chlororesorcinol;1-naphthol; 1,5-dihydroxynaphthalene; 2,7-dihydroxynaphthalene;2-methylresorcinol; 1-hydroxy-6-aminonaphthalene-3-sulfonic acid; thymol(2-isopropyl-5-methylphenol); 2-chlororesorcinol;2,3-dihydroxy-1,4-naphthoquinone; and 1-naphthol-4-sulfonic acid;m-phenylenediamine; 2-(2,4-diaminophenoxy)ethanol;N,N-bis(hydroxyethyl)-m-phenylenediamine; 2,6-diaminotoluene;N,N-bis(hydroxyethyl)-2,4-diaminophenetole;bis(2,4-diaminophenoxy)-1,3-propane; 1-hydroxyethyl-2,4-diaminobenzene;2-amino-4 hydroxyethylaminoanisole; aminoethoxy-2,4-diaminobenzene; 2,4diaminophenoxyacetic acid; 4,6-bis(hydroxyethoxy)-m-phenylenediamine;2,4-diamino-5-methylphenetole; 2,4-diamino-5-hydroxyethoxytoluene;2,4-dimethoxy 1,3-diaminobenzene; 2,6-bis(hydroxyethylamino) toluene;m-aminophenol; 2-hydroxy-4-carbamoylmethylaminotoluene;m-carbamoylmethylaminophenol; 6-hydroxybenzomorpholine;2-hydroxy-4-aminotoluene; 2-hydroxy-4-hydroxyethylaminotoluene;4,6-dichloro-m-aminophenol; 2-methyl-m-aminophenol;2-chloro-6-methyl-m-aminophenol; 2-hydroxyethoxy-5-aminophenol;2-chloro-5-trifluoroethylaminophenol; 4-chloro-6-methyl-m-aminophenol;N-cyclopentyl-3-aminophenol;N-hydroxyethyl-4-methoxy-2-methyl-m-aminophenol;5-amino-4-methoxy-2-methylphenol; 1-phenyl-3-methyl-5-pyrazolone;5-hydroxy-1,4-benzodioxane; 3,4-methylenedioxyphenol;2,6-dihydroxy-3,4-dimethylpyridine; 3,5-diamino-2,6-dimethoxypyridine;2,6-bis-hydroxyethoxy-3,5-diaminopyridine;3-amino-5-hydroxy-2,6-dimethoxypyridine; 4-hydroxyindole;6-hydroxyindole; 2-amino-3-hydroxypyridine; 2,6-diaminopyridine;5-(3,5-diamino-2-pyridyloxy)-1,3-dihydroxypentane;3-(3,5-diamino-2-pyridyloxy)-2-hydroxypropanol; 4-hydroxyindoline;6-hydroxyindoline; o-aminophenol or combinations thereof.

Preferred couplers for use in the invention include: o-aminophenol;resorcinol; m-aminophenol; 5-amino-2-methylphenol; 2-methyresorcinol;1-napthol; 2-methyl-1-napthol; 2-(2,4-diamino-phenoxy)ethanol;1-phenyl-3-methyl-5-pyrazolone; m-phenylenediamine; 4-hydroxyindole;6-hydroxyindole; 4 chlororesorcinol; 2-chlororesorcinol;2,6-diaminotoluene; 4-hydroxyindoline; 6-hydroxyindoline; o-aminophenol;1phenyl-3-methyl-5-pyrazoline; 2,6-diaminopyridine; and mixturesthereof.

The most preferred couplers are o-aminophenol; 1-naphthol;2-methylresorcinol; resorcinol; m-aminophenol; 5-amino-2-methylphenol;2(2,4-diaminophenoxy)-ethanol; m-phenylenediamine;1-phenyl-3-methyl-5-pyrazolone; 2,6,-diaminopyridine and mixturesthereof.

The coupler is generally present in the precursor mixture at a levelfrom about 0.005 wt % to about 10 wt %, preferably from about 0.01 toabout 5 wt %, and most preferably from about 0.01 to about 4 wt %.

The weight ratio of primary intermediate to coupler is generally in therange from about 100 to about 0.01, preferably from about 50 to about0.05 and most preferably from about 10 to about 0.1.

It should be understood that the descriptions of primary intermediatesand couplers given above are meant to implicitly include the salt formsof those dye molecules that form stable salts. For example, thehydrochloride or sulfate salts in the case of amines, and the alkalimetal salts in the case of phenols.

Solubility Enhancers

Water is the preferred principal solvent, carrier or diluent for thecompositions according to the present invention. As such, thecompositions according to the present invention may include one or moresolubility enhancers as defined above. Generally, two preferred classesof solubility enhancers are solvents and surfactant systems.

Preferred solvents are miscible with water and innocuous to the skin.Solvents suitable for use herein include C₁-C₁₀ mono- or polyhydricalcohols and their ethers, glycerine, monohydric and dihydric alcoholsand their ethers. In these compounds, alcoholic residues containing 2 to6 carbon atoms are preferred. Thus, a particularly preferred groupincludes ethanol, isopropanol, n-propanol, butanol, propylene glycol,ethylene glycol monoethyl ether, hexylene glycol and mixtures thereof.

The solvents may be present in the precursor mixture at a level of fromabout 0.1 to 20 wt %, preferably from about 0.1 to about 15 wt % andmost preferably from about 0.5 to 10 wt %.

The second class of solubility enhancer useful in the present inventionis surfactants.

A particularly suitable class of surfactants is cationic surfactants.One type of preferred cationic surfactant is amine based and includesalkyl amines, alkylethoxy amines, ethoxylated alkyl amines and alkylalkanol amines. Preferred alkyl groups have 1 to about 22 carbon atomsand can have a mixture of chain lengths, e.g., methyl and hexadecyl. Theterm amines include primary, secondary, tertiary and quaternary amines.

A second type of preferred cationic surfactant is amidoamines andincludes C12-C22 alkyl or alkylethoxy mono, di and higher (poly)amidoamines which can be ethoxylated or unethoxylated. Examples includesodium dimethylaminopropyl cocoaspartamide, cocoamidopropyldimethylamine, olivamidopropyl dimethylamine, soyamidopropyldimethylamine, tallowamidopropyl dimethylamine, stearamidoethyldimethylamine and mixtures thereof.

Another preferred class of surfactant that is suitable for use as asolubility enhancer is nonionic surfactants. This class includes longchain fatty alcohols, mono, di and triglyceride and their derivatives,long chain (C12-C18) alcohol ethoxylates and mixtures thereof. Examplesinclude: steareth 20, oleth 10, laureth 4, PEG-12 glyceryl dioleate,glycerol stearate, sorbitan oleate, PPG-9 buteth-12 and mixturesthereof.

The level of surfactants used as solubility enhancers in the dyeprecursor mixture can generally range from 0.1 to about 30 wt %,preferably from about 0.2% to about 20 wt % and most preferably fromabout 0.25 to about 15 wt %.

Both solvents and surfactants can and often are combined to achieve thedesired state of solubility of the primary intermediate and coupler inthe dye precursor mixture. However, it has been found that the type andlevel of solubility enhancer affect the ability of the oxidative dyes toabsorb into the hair fibers and be retained after application of anappropriate electrical potential. Although this can be difficult topredict, the optimum type and level of solubility enhancer can bedetermined empirically by treating a standard hair sample undercontrolled conditions with a precursor mixture and developing the colorwith an electrode system under standardized conditions. One such testprotocol is the In-Vitro Color Retention Test and is described below. Asdiscussed below, ΔE is the distance between two colors in theTristimulus color space. Thus, ΔE is the change in color of the testhair sample after treatment with the precursor solution and oxidized bymeans of application of a 3V direct current for a set period of time 30min. It has been found that the level and type of solubility enhancerused in the precursor solution should be such that this mixture providesa color change, AE, of at least about 0.15 when measured by the In-vitroColor Retention Test described below.

pH Control Agents

The dye precursor mixture has a pH that can range from about 5 to about11, preferably from about 7 to about 10. It is preferable to avoid anacidic pH below about 5 because the rate of electrochemical coloringdecreases and also because acidic solutions tend to be damaging to thehair.

Adjustment of pH can be effected by using well known acidic or basicbuffering agents used for controlling pH in the field of treatingkeratinous fibers, and in particular human hair.

Possible acidic pH control agents include inorganic and organic acidssuch as hydrochloric acid, tartaric acid, citric acid, and carboxylic orsulphonic acids such as ascorbic acid, acetic acid, adipic acid, lacticacid, sulfuric acid, formic acid, ammonium sulfate and sodiumdihydrogenphosphate/phosphoric acid, disodium hydrogenphosphate/phosphoric acid, potassium chloride/hydrochloric acid,potassium dihydrogen phthalate/hydrochloric acid, sodiumcitrate/hydrochloric acid, potassium dihydrogen citrate/hydrochloricacid, potassium dihydrogencitrate/citric acid, sodium citrate/citricacid, sodium tartrate/tartaric acid, sodium lactate/lactic acid, sodiumacetate/acetic acid, disodium hydrogenphosphate/citric acid and sodiumchloride/glycine/hydrochloric acid and mixtures thereof.

Still other organic acids include maleic acid, malic acid, succinicacid, glycolic acid, glutaric acid, benzoic acid, malonic acid,salicylic acid, gluconic acid, polyacrylic acid, their salts, andmixtures thereof.

Especially preferred acidic pH control agents for use in the dyeprecursor mixture include citric acid, lactic acid, glycolic acid,acetic acid, phosphoric acid and mixtures thereof. These materials donot have the potential of generating noxious gasses through theapplication of a potential by the electrode system of the presentinvention.

Several different basic pH control agents can be used to adjust the pHof dye precursor mixture of the present invention (both in storage andat point of use). Non-limiting examples of suitable basic bufferingagents are ammonium hydroxide, urea, ethylamine, dipropylamine,triethylamine and alkanediamines such as 1,3-diaminopropane, anhydrousalkaline alkanolamines such as, mono or di- or tri-ethanolamine,preferably those which are completely substituted on the amine groupsuch as dimethylaminoethanol, polyalkylene polyamines such asdiethylenetriamine or a heterocyclic amine such as morpholine as well asthe hydroxides of alkali metals, such as sodium and potassium hydroxide,hydroxides of alkali earth metals, such as magnesium and calciumhydroxide, basic amino acids such as L-arginine, lysine, oxylysine andhistidine and alkanolamines such as dimethylaminoethanol andaminoalkylpropanediol and mixtures thereof. Also suitable for use hereinare compounds that form HCO₃ ⁻ by dissociation in water (hereinafterreferred to as ‘ion forming compounds’). Non-limiting examples ofsuitable ion forming compounds are Na₂CO₃, NaHCO₃, K₂CO₃, (NH₄)₂CO₃,NH₄HCO₃, CaCO₃ and Ca(HCO₃)₂ and mixtures thereof.

Certain alkaline buffering agents such as ammonium hydroxide andmonoethanolamine (MEA), urea and the like, can also act as hair swellingagents (HSA's).

Preferred alkaline or basic pH control agents for the dye precursorcompositions according to the present invention, is ammonium hydroxide,sodium hydroxide, sodium carbonate, sodium carbamate and mixturesthereof.

The level of pH control agent used in the dye precursor mixture cangenerally range from a value of about 0.2 wt % to about 20 wt %,preferably from about 0.5 to about 18 wt % and most preferably from 1 toabout 15 wt %.

Supporting Electrolyte

The precursor mixture also preferably contains a supporting electrolyteto provide the mixture with an adequate electrical conductivity. Thesupporting electrolyte is preferably an electrochemically inert salt.They can comprise species present or formed by the pH control orbuffering agents described above or they can be salts added in additionto these buffering agents.

Preferred additional supporting electrolytes include perchorates,sulfates, borates and their mixtures. The level of additional supportingelectrolyte in the oxidative dye precursor mixture ranges from about 1to about 25% preferably about 1% to about 15% and most preferably about5% to about 15% by weight of the precursor mixture.

Thickeners

Thickeners may be optionally included in the oxidation hair colorantcompositions of the invention. Long chain fatty alcohols having fromabout 11 to about 18 carbon atoms in the long fatty chain can bethickener constituents of the compositions of this invention. Thesealcohols can be used alone, or in admixture with each other. Whenincluded in the compositions, the alcohol is preferably present at fromabout 0.5 to about 10 weight percent of the composition, and morepreferably at from about 2 to about 8 weight percent.

Lauryl alcohol, oleyl alcohol, myristyl alcohol, stearyl alcohol, andthe like, and mixtures thereof are contemplated herein as thickeners. Inaddition, mixtures of natural or synthetic fatty alcohols having fattychain lengths of from about 11 to about 18 carbons are also useful.Several such mixtures are available commercially, and are exemplified bythe material containing a mixture of synthetic alcohols with 12 to 15carbons in the alkyl chain sold under the trademark NEODOL 25 by ShellChemical Company, and the material containing a mixture of syntheticalcohols with chain lengths of 12 to 16 carbons sold under the trademarkALFOL 1216 Alcohol by Conoco Chemicals.

Thickening agents suitable for use in the compositions herein may alsobe selected from oleic acid, cetyl alcohol, oleyl alcohol, sodiumchloride, cetearyl alcohol, stearyl alcohol.

Fatty alcohols of the above discussed carbon chain lengths which areethoxylated to contain an average of one or two moles of ethylene oxideper mole of fatty alcohol can be used in place of the fatty alcoholsthemselves. Examples of such useful ethoxylated fatty acids includeethylene glycol cetyl ether, polyoxyethylene (2) stearyl ether, and thelike; the exemplary compounds having CTFA Dictionary names of Ceteth-1and Steareth-2, respectively.

Particularly useful thickeners for compositions used for electrochemicalcoloring form conducting gels that are shear thinning yet quicklyrecover viscosity when the shear is removed. This allows the preferredelectrode systems that are in the form of a comb or brush (i.e., thathave multiple electrodes) to be passed repeatedly through the hairwithout the dripping of the precursor mixture. Gel forming syntheticthickeners include CARBOPOL, ACULYN 28, STRUCTURE 2001, 3001, and XL,ACROSYL, SALCARE inversion type thickeners such as SALCARE SC 91 andmixtures thereof. Preferred thickeners for use herein are ACULYN 22(RTM), steareth-20 methacrylate copolymer; ACULYN 44 (RTM) polyurethaneresin and ACUSOL 830 (RTM), acrylates copolymer that are available fromRohm and Haas, Philadelphia, Pa., USA. Additional thickening agentssuitable for use herein include sodium alginate or gum arabic, orcellulose derivatives, such as methylcellulose or the sodium salt ofcarboxymethylcellulose or acrylic polymers.

Optional Ingredients

The dye precursor compositions of the present invention can comprise awide range of optional ingredients. Examples of these functional classesinclude: mildness enhancers such as cholesterol and its derivatives,hair swelling agents, anticaking agents, antioxidants, binders,biological additives, bulking agents, chelating agents, chemicaladditives, colorants, cosmetic astringents, cosmetic biocides,denaturants, drug astringents, emulsifiers, film formers, fragrancecomponents, humectants, opacifying agents, plasticizers, preservatives,propellants, reducing agents, solvents, foam boosters, hydrotropes,solubilizing agents, suspending agents (nonsurfactant), sunscreenagents, ultraviolet light absorbers, and viscosity increasing agents(aqueous and nonaqueous), and hair fiber lubricants. Examples of otherfunctional classes of materials useful in the art include solubilizingagents, sequestrants, amino acids, hydrolyzed proteins and the like.

It may also be advantageous to include agents that condition the hair toimprove combability and impart a silky/moisturized feel to the hairafter it dries. Such agents include fatty long chain amines and theirderivatives, silicones such as dimethicone and amodimethicone, longchain fatty acohols, cationic conditioning polymers, and mixtures ofthese materials. Such conditioners can be incorporated in either theprecursor mixture, or even be delivered in the aligning step (see below)as part of the aligning means as is known in the art. Conditioners canalso be packaged separately when kits are employed.

Although the electrochemical method described herein is capable ofdyeing the hair without the need for chemical oxidants, the dyeprecursor solution may also include an oxidizing agent such as hydrogenperoxide. It is preferable, however to limit the level of oxidizingagent to less than 50%, more preferably less than 25% and mostpreferably less than 10% of the amount required to oxidize the dyeprecursors present in the composition.

It should be understood that the above list of ingredients is intendedto illustrate the types on materials that can be incorporated. However,it is important to select materials that do not interfere with theelectrochemical oxidation of the primary intermediate or that generatenoxious or unwanted by-products. A person skilled in the art should becapable of selecting appropriate material having understood theprinciples of the instant invention.

Electrode System

The second element of the invention is an electrode system capable ofoxidizing at least one of the primary intermediates in the dye precursormixture. Preferably at least 50%, more preferably 75% and mostpreferable at least 90% of the colored dye molecules that are formed,are formed electrochemically and not by chemical oxidation from either ableach or oxygen present in the air or generated electrochemically.

In simplest terms, the electrode system is comprised of conductingelectrodes that contact the precursor mixture that is on the hair, apower supply connected to these electrodes, and an insulated handle/baseassembly. These components are described below. The electrode system caneither be a simple disposable one-use devise or be a multi-use devise ofa more robust and durable construction.

Electrodes

The electrodes are preferably inert (in an electrochemical sense)conducting wires, plates, cylinders or other shapes that are brought incontact with the hair on which has been applied the precursor mixture.When a voltage is applied to the electrodes that exceeds the netelectrolytic potential, oxidation of a primary intermediate will occurat the anode (e.g., the electrode in contact with the positive end of abattery), and reduction of water to hydrogen gas will occur at thecathode.

In principle, the electrodes can be a single anode/cathode pair, e.g.,two wires. However, it is preferable to have a multiplicity of anodesand cathodes and even more preferable to combine or integrate theelectrodes with a hair aligning and distributing means such as a comb, apick, a brush or a mixture of these elements. This combination allowsthe user to efficiently initiate the oxidation of the primaryintermediate and to uniformly distribute the dye molecules on the hair.The combined element also allows a more accurate control of the locationof hair coloring, which is critical for coloring visible roots, orcreating highlights.

Alignment means that have at least one comb or one brush element areespecially preferred. The comb is an implement of grooming dating fromancient times yet patents on various improvements continue to appear. Asused here a comb element consists of strip of material on which areaffixed one or more rows of teeth or tines. The comb element can be ofsimple construction or it can be contoured or have features that inducehighlighting, for example, variable spacing or length of the teeth orwells cut into the fixing strip.

A brush element as defined herein is an aligning means that has bristlesset into a handle. The handle can be rigid or flexible. The bristles canbe single rigid filaments or tines, flexible fibers, or tufts of fibers.The bristles can be of uniform length or they can be of differentlengths either to allow the brush element to promote highlightingeffects by opening channels or different depths or to allow the brush tobe contoured to conform to the shape of the head. The brush can alsoincorporate step features which further promote highlighting, such as isdisclosed in U.S. Pat. No. 6,453,909 B1, which is hereby incorporated byreference. Further, the bristles can be distributed in rows in a planarconfiguration or radially distributed to form an arc.

The aligning means can also comprise a combination to theabove-described elements. Combinations of brush and comb elements arewell known in the art and an early example may be found in U.S. Pat. No.660,893.

Thus, in a preferred embodiment of the electrode system of theinvention, some or all of the teeth, tines, filaments, or bristles ofthe comb or brush elements are capable of conducting electricity andserve as electrodes when connected to the power supply. These conductingtines, filaments or bristles can be simply constructed of a conductingmetal such as stainless steel, or a suitable alloy, or they can becomprised of a thin coating of a conducting metal deposited of asubstrate such as plastic. In the latter case for example, theconducting coating can be gold, silver, platinum, palladium, molybdenum,tin oxide or other metal that would be suitable as an electrode. Thecoating can also be a conducting polymer.

Although any number of anodes and cathodes can be employed in theelectrode system of the invention, it is preferable that the totalsurface area of the anodes is greater that the total surface area of thecathodes. Preferably the surface area of the anodes exposed to theprecursor mixture on the hair should be about 1.5 and more preferablytwice the total surface area of the cathodes. This can be accomplishedfor example by having the number of anodes (or anodic tines, teeth,filaments, or bristles) exceed the number of cathodes (or cathodictines, teeth, filaments, or bristles). Further, the anodes can beroughened or have a high surface area porous coating applied to theirsurface.

The reason for having the total anode surface area exceed the totalcathode surface area is related to the possible redox reactions that canoccur at the cathode. As discussed above, reactive intermediates thatare generated at the anode quickly migrate away from the anode towardsthe cathode. Most of these reactive species (i.e., free radicals) canthen react quickly with primary intermediates and couplers to generatecolored molecules. However, some radicals can survive in solution andreach the cathode. Since the reduction potential of many of theseintermediates is more positive than the reduction potential of water inalkaline solution they can be preferentially reduced back to the primaryintermediate. This wasteful reduction of reactive intermediates can beminimized by having the surface area of the anodes exceed the surfacearea of the cathodes. However, this has to be balanced against thecurrent carrying capacity of the electrode system and the fieldstrength, which decrease as the surface areas of the anodes and cathodesdiverge, and average distance between anode and cathode increase. Inpractice, the surface area ratio is preferably between about 1.5 andabout 4.

The cathodes and anodes can also be of different lengths to penetratedifferent depths or layers of hair and further reduce the loss ofradicals by the reduction process described above.

Preferably, the electrodes should also have some resistance topolarization such that the average field strength (voltage divided byaverage cathode-anode distance) remains reasonably constant (90% ofinitial value) for at least about 5 minutes and preferably for at leastabout 10 minutes of continuous use. The electrodes can optionally becoated with a precious transition metal layer such as, for example,palladium, that reduces their susceptibility to polarization.

Although for cost reasons it is preferable that the electrodes have asimple construction, they can also include porous coatings with addedfunctionality. For example, the cathode can be coated with a porous saltbridge impregnated with an electrolyte to further isolate the reactiveintermediates and prevent their reduction. The electrodes can also becoated with metal oxides such as tin oxide that absorb gaseouselectrolysis products. Still further, the cathode can be comprised of aself-contained standard half cell which will circumvent to reduction ofwater.

It is emphasized that the electrode system need not be combined with analigning means and can have a more complicated structure. For example itcan comprise a cloth mesh or plastic bonnet into which electrodes areembedded or affixed. The consumer wears the bonnet for a fixed period oftime during which the electrochemical oxidation takes place.

Power Supply

The electrodes described above are connected to a power supply by meansof suitable “wiring”. The power supply can be any means of deliveringthe minimum voltage required to oxidize at least one of the primaryintermediates to form a reactive species. A direct current (DC) sourceis preferred. The power supply can be comprised of a simple disposablebattery or batteries, a rechargeable battery, or it can utilize an AC toDC converter to generate the required potential and current.

Disposable batteries include multiple-use batteries such as standard 3V(or higher) AAA, C or D alkaline cells or miniature batteries havingsufficient storage for a single use.

Rechargeable batteries can also be employed and the recharger can be apart of the electrode system of can be a separate unit to which theelectrode system is coupled.

It is preferable for safety and performance reasons to employ directcurrent. Normal AC current can be converted by means of readilyavailable AC to DC converters that provide suitable voltage and currentfor use in electrochemical hair coloring, e.g., about 10 mV to about 3 Vand about 10 mA to about 1.5 A respectively.

The power supply can also be a storage device that can be chargedthrough direct mechanical action.

Handle/Base Assembly

The handle and base assembly provides an insulated means to hold thedevice and to affix the electrodes. The handle can comprise acompartment for the power supply (e.g., disposable or rechargeablebattery) and the internal wiring that connects the power supply to theelectrodes.

The handle can be constructed of any suitable insulating material suchas plastic or wood. As stated above, it is preferable to integrate theelectrodes with an aligning and distributing means so as to form aconvenient implement to electrochemically color the hair. It may beconvenient in this case to integrate the teeth, tines, filaments orbristles with the base assembly and handle to have a unitary materialdesign, i.e., all or most of the components can be assembled in one ortwo steps.

The internal wiring can be in the form of true wires or can be by meansof thin films of metal coated on plastic like the design used in thefabrication of integrated circuits. The handle and base assembly canalso incorporate features useful in styling the hair such as a“rat-tail”.

The handle and base assembly can also incorporate other electricalcomponents such as a switch, an on-off indicator light, a means ofconnection to AC current through an AC to DC converter, a re-chargerport, and current/voltage regulators. The handle/base assembly can alsoincorporate a device to convert mechanical energy to electrical energy.

The handle and base assembly may also incorporate a variable voltageadjustment feature, e.g., a rheostat that allows the consumer to moregradually develop color or to achieve different shades according to ascale or guide supplied with the implement or kit.

The handle and base assembly can also include a reservoir thatsimultaneously dispenses the precursor mixture and applies the requiredpotential to electrochemically develop the color. Several types of comband brush implements are disclosed in the art that incorporate reservoirfeatures and these can be adapted to function with the electrochemicaldyeing process described herein.

Examples of Electrode System Designs

FIG. 1 is a side view schematic illustration of an electrode system forthe electrochemical dyeing of hair wherein the electrodes are combinedwith a comb hair aligning means and the power supply is a disposablebattery. The anodic tines 6 are connected via a separate circuit 4 tothe positive terminal of a battery 1. The fewer cathodic tines 7 areconnected to the negative terminal of the battery via a separate circuit5 which includes a switch 3 and an indicator light 2. The tines 6, 7 areaffixed to an insulated base assembly 8 which is attached to aninsulated handle 9.

FIG. 2 is a schematic of an electrode system for the electrochemicaldyeing of hair wherein the electrodes are combined with a brush aligningmeans and the power supply is provided from AC current by means of an ACto DC converter. FIG. 2A is a side view schematic. Here the multipleanode filaments 9, and fewer cathode filaments 10, are fixed to thehousing assembly 11 and are attached through separate circuits 7 and 8connected to a DC power source. An AC to DC converter 1 has standardprongs compatible with an electrical socket 2. The wire 3 is connectedto a switch 4 and an indicator light, which is attached to the handle 6.Note that in this case the cathode and anode elements are of differentlengths. FIG. 2B is a bottom view of part of the housing assembly 11showing the arrangement of combination electrode-filaments.

APPLICATION OF METHODS AND COMPOSITIONS OF THE INVENTION

The dye precursor mixture of the present invention is first applied tohair followed by application of the electrode system that is preferablycombined with a means for aligning and distributing the hair. Althoughthe electrode system can be applied immediately, it is often preferableto allow the precursor mixture to remain in contact with the hair for aperiod of time ranging from about 30 seconds to about 60 minutes.Without wishing to be bound by theory, this contact time allows part ofthe precursors to diffuse into the hair fibers. Following theapplication of the electrode system and the achievement of the desiredcolor, the hair is rinsed, and if desired a separate hair conditionercan be applied. However, hair-conditioning agents can also beincorporated in the precursor mixture obviating the need for a separateconditioning step.

The process described above is in sharp contrast to conventionalpermanent hair coloring methods which require that the hair be contactedwith a dye precursor composition and a hair color developer composition,simultaneously or sequentially.

The electrochemical process can be used to color the entire hair.However, it also provides a convenient means to selectively colorportions of the hair in a highly controlled manner. The process isespecially convenient for touching up visible roots as the hair growsthus prolonging the time between complete hair coloring. Here, theprecursor mixture can be applied to the root area by means of packagefitted with an elongated dispensing nozzle. A specialized “touch-up”electrode system in the form of a comb is then applied to the desiredareas. It should be understood that the electrode system could alsoinclude a reservoir for the precursor mixture so that the coloringprocess can be achieved in one step.

The process can also be used to selectively highlight the hair withdifferent color streaks. This can be achieved ether by applyingdifferent primary intermediate/coupler mixtures or in principle byvarying the voltage so as to favor different chemical reactions. Here,an electrode system that incorporates a styling feature is desirable(e.g., tines of different lengths or specialized arrangement of anodesand cathodes to favor surface dyeing or layering). Again, the stylingelectrode system can incorporate a reservoir feature that dispenses theprecursor mixture.

Evaluation Methodology

Assessment of Initial Color and Color Change

The equipment used to measure both the initial color and color change onsubstrates dyed by the electrochemical coloring process described hereinis a Hunter spectrophotometer. The value used to express the degree ofcolor change induced by the combined treatment of precursor mixture andelectrode system on any particular hair substrate is ΔE. The term ΔE, asdefined herein, represents the distance in color space between twodifferent samples, e.g., before and after treatment. ΔE is computed fromthe measured changes of the Tristimulus vales ΔL, Δa, and Δb valuesmeasured with the spectrophotometer by the equation:ΔE=difference of color of treated and non-dyed hair: ΔE={square root}(ΔL² +Δa ² +Δb ²)where L is a measure of lightness and darkness (color intensity),wherein L=100 is equivalent to white, and L=0 is equivalent to black.Further, ‘a’ is a measure of the red and green quotients (color hues)such that positive equates to red and negative equates to green, and ‘b’is a measure of the yellow and blue quotients (color hues) such thatpositive equates to yellow and negative equates to blue.Piedmont In-Vitro Color Retention Test

A 1 gm tress Piedmont hair from International Hair Products Inc. isfirst treated with the aqueous dye precursor composition at a level ofbetween 1.5 to 3 gm precursor mixture per gm of hair. The precursor isdistributed over the hair surface by means of a styling brush of thetype commonly employed by salon stylists. After 30 sec. to about 30 minfrom the completion of the application of the precursor composition, thewet hair is contacted with two electrodes having a potential differenceof 3 volts that is provided by a constant direct current (DC) source fordifferent time periods. Rinsing and drying the hair under standardconditions follows this.

The hair tresses are dried for about 30 minutes and the values of L, a,and b, are then measured and the change in color index, ΔE, of the tresscompared to its initial value is then computed from the above equation.

It has been found that the color change produced by oxidative dyes candepend on the chemical environment provided by the precursor mixturewhen it comes into contact with the hair. Precursor mixtures useful inthe present invention should at least be capable of producing a colorchange, ΔE, of at least 0.15 units when used in the above testprocedure.

The resistance of the treatment to fading by for example shampootreatment can also be measured in a similar way. After the above dyetreatments, the dried hair tresses are placed in a tube containing a 10%shampoo solution and agitated for 1 hour by means of a mechanicalshaker. The tresses are then rinsed and dried. The values of L, a, andb, are then measured and the change in color index, ΔE, is computed andcompared to their value before shampoo extraction or to the initialuntreated hair as desired.

EXAMPLES

The following examples are shown as illustrations only and are notintended to limit the scope of the invention.

Example 1 Electrochemical Coloring of Hair Using 1,4-phenylene Diamine(PPD) and 2-methyl 4-aminophenol (PAOC) at pH 7

This example illustrates the coloring of hair with oxidative dyeswithout the use of peroxide and alkaline solutions like ammonia by usingan electrode system to initiate and drive the coupling reaction.

Two tresses (0.5 gm) of Piedmont hair were placed in 5 ml of an aqueousmixture whose composition is shown in Table 1 A. In this case theprimary intermediate is PPD and the coupler is PAOC. The pH of themixture was 7.0.

A voltage of 3 V was applied to the precursor mixture on the hair bycontacting it with two wires connected to a dry cell battery. After 30minutes the electrodes were removed and the hair swatch was rinsed withwater and allowed to dry.

The above procedure was repeated with a mixture having exactly the samecomposition and also for the same time but in this case the electricalleads were not connected to the battery (i.e., 0V).

The changes in color resulting from these two procedures are compared inTable 1B. It is seen that the change in color index is over twice aslarge for the hair samples in which a voltage was applied with a singleanode-cathode pair. It is also of note that this example alsoillustrates that the electrochemical hair coloring method of theinvention does not require either hydrogen peroxide or ammonia. TABLE 1ADye precursor mixtures used in Example 1 I A. Dye precursor mixtureIngredients Wt % pH 1,4-phenylene diamine (PPD) 0.3 7.02-methyl-4-aminophenol (PAOC) 0.35 Isopropanol 10 Supporting electrolyte(sodium 2.0 perchorate) Deionized water to 100%

TABLE 1B Change in color after electrochemical treatment Vs a controlChange in Tristimulus values relative to Change in Color Treatmentuntreated Hair^(a) Index, ΔE^(a) Example 1 Electrochemical coloring ΔL =−30.6 ΔE = 35 for 30 minutes @ 3 volts Δa = 13.8 (single anode-cathodepair, Δb = −10.0 pH = 7) Comparative Example No current passed throughΔL = −10 ΔE = 14.5 solution Δa = 8.5 Δb = −6.1^(a)“ΔL” represents the change in color intensity, “Δa” represents thechange in the ratio of red and green hue and “Δb” represents the changein the ratio of yellow and blue hue of the color. ΔE is equal to thesquare root of the sum of the squares of ΔL, Δa, and Δb.

Example 2 Electrochemical Coloring of Hair Using Several Oxidative Dyesat pH 10

This example illustrates the invention using another primaryintermediate and coupler. The example also demonstrates that a coupleralone is not sufficient for electrochemically coloring hair in theabsence of a primary intermediate.

In Example 2A-2I tresses (0.5 gm) of Piedmont hair were separatelyplaced in 5 ml of the aqueous mixtures whose composition are shown inTable 2. The pH of all the mixtures was 10.0. A voltage indicated in theTable 2 was applied to the precursor mixture on the hair by contactingit with two wires connected to a dry cell battery. After 30 minutes theelectrodes were removed and the hair tress was rinsed with water andallowed to dry. The changes in color are given in Table 2.

It is seen from Table 2 that 1,4-phenylenediamine/2-methyl-4-aminophenol and the 1,4-phenylenediamine/Resorcinoland N,N-bis-dihydroxyethyl/1-naphthol, p-phenylene diamine primaryintermediate-coupler pairs are activated albeit to varying degrees bythe application of an electrical potential (compare 3V with 0V: Examples2A Vs 2B, 2D Vs 2E, and 2G Vs 2H). However, use of the couplers bythemselves are not effective in electrochemically coloring the hair—theprimary intermediate must also be present, e.g., Examples 2A Vs 2C, 2DVs 2F.

It should be noted that not all the dye pairs exhibit the samedifference between the “0” current and 3 Volt color changes. Withoutwishing to be bound by theory, the differences are probably related tothe ease of air oxidation of each dye (no doubt catalyzed by transitionmetal ions present in the hair), i.e., their oxidation potentials underthe conditions tested. Examples 2J-2L support this conclusion. At pH 10where 3-Methyl-4-Aminophenol oxidizes to a limited extent even in air,the differences are small. However, at pH 7 where the oxidationpotential is less positive, electrochemical oxidation produces a largerrelative effect. TABLE 2 Dye precursor mixtures used in Example 2 andresults Examples Ingredients Ex 2A Ex 2B Ex 2C Ex 2D Ex 2E Ex 2F Ex 2GEx 2H Ex 2I Ex 2J Ex 2K Ex 2L 1,4-phenylene diamine 0.3 0.3 0.2 0.22-methyl-4-aminophenol 0.35 0.35 0.35 0.3 0.3 0.3 0.3 (p-amino-o-cresol)Resorcinol 0.21 0.21 0.21 3-Methyl-4- 0.3 0.3 0.3 0.3 AminophenolN,N-bis-dihydroxyethyl, 0.2 0.2 p-phenylene diamine 1-napthol 0.2 0.2NaOH to pH 10 x x x x x x x x x x Applied Voltage 3 V 0 V 3 V? 3 V 0 V 3V 3 V 0 V 3 V 0 V 3 V 0 V pH 10 10 10 10 10 10 10 10 10 10 7 7 Change inTristimulus values ΔL −37.1 −14.9 −5.8 −32.1 −12.4 −9.8 −28.5 −25 −27.8−20.3 −19 −7.4 Δa 14.4 10.6 2.1 1.8 2.7 0.24 −7.2 −7.0 22.1 20.5 −14.2−7.1 Δb −15 −4.9 −0.2 2.5 −6.8 −3.2 −28.7 −26.2 −2.0 −2.9 0 1.9 Changein Color Index ΔE 42.5 18.9 6.2 32.1 14.4 10.3 41.1 36.8 34.4 35.7 29.922.6

Example 3 Comparison of Direct Electrochemical Oxidation to the PossibleIndirect Oxidation Through the Generation of Molecular Oxygen

As discussed above, the direct oxidation of the primary intermediatesuseful in the instant invention, is favored over the oxidation of waterto molecular oxygen. This example demonstrates that even if this werenot the case, any molecular oxygen that might be generated would lead toonly slight oxidation if at all.

A solution of comprising 0.1 wt % 1,4-phenylene diamine and 0.11 wt %2-methyl -4-aminophenol, 1-5 wt % sodium perchlorate at pH 7 wasprepared and divided into two parts. Both parts were initially colorlessto the eye.

An electrode pair was inserted into one part and a potential of 3V wasapplied for 10 minutes. This mixture became highly colored.

Oxygen gas was bubbled into the other part also for 10 minutes. Thesolution remained colorless to the eye.

The UV-Vis absorbance at a wavelength of about 490 nm exhibited a 2.5fold higher absorbance for the electrolyzed sample with the oxygenbubbled sample exhibiting a very shallow peak indicating little, if any,conversion of the precursors to indo dye.

This indicates that electrochemical dyeing is the direct oxidation ofthe dye at the anode and not the indirect oxidation by molecular oxygenas had been proposed by Larsky et al. in U.S. Pat. No. 5,472,456.

Example 4 pH Dependence of Electrochemical Hair Coloring

Tresses of Piedmont hair (5 gm) were treated with solution containing0.3 wt % 1,4-phenylene diamine and 0.35 wt % 2-methyl-4-aminophenoladjusted to pH 7, 9 or 10 with sodium hydroxide. A potential of 3V wasapplied to the precursor mixture on the hair by contacting it with twowires connected to a dry cell battery. After 30 minutes the electrodeswere removed and the hair swatch was rinsed with water and allowed todry. The changes in color are given in Table 3A.

Similar experiment were carried out with 1,4-phenylenediamine/resorcinol and N,N-bis-dihydroxyethyl,p-phenylene diamine and1-napthol buffered at to different pH values. The changes in color aregiven in Table 3B and Table 3C respectively.

In the case of both the 1,4-phenylene diamine/2-methyl-4-aminophenol andthe 1,4-phenylene diamine/resorcinol dye precursor pairs the change incolor is much greater at pH greater than or equal to 9 as compared to pH7. TABLE 3A Effect of treatment pH on the electrochemical coloring ofhair with 1,4-phenylene diamine/2-methyl-4-aminophenol Change inTristimulus values relative to Change in Color Treatment pH untreatedHair Index, ΔE 7 ΔL = −30.6 ΔE = 35 Δa = 13.8 Δb = −10.0 9 ΔL = −37.8 ΔE= 43.0 Δa = 15.8 Δb = −13.1 10 ΔL = −37.1 ΔE = 42.6 Δa = 14.4 Δb = −15.0

TABLE 3B Effect of treatment pH on the electrochemical coloring of hairwith 1,4-phenylene diamine and resorcinol (0.3/0.35 wt % respectively)Change in Tristimulus values relative to Change in Color Treatment pHuntreated Hair Index, ΔE 7 ΔL = −16.5 ΔE = 17.7 Δa = 2.4 Δb = −1.9 8 ΔL= −23.5 ΔE = 23.7 Δa = 2.2 Δb = −0.7 9 ΔL = −31.9 ΔE = 32.5 Δa = 2.2 Δb= −6.2 10 ΔL = −32.1 ΔE = 32.9 Δa = 1.8 Δb = −6.8

TABLE 3C Effect of treatment pH on the electrochemical coloring of hairwith N,N-bis-dihydroxyethyl, p-phenylene diamine and 1-napthol (0.2/0.2wt % respectively) Change in Tristimulus values relative to Change inColor Treatment pH untreated Hair Index, ΔE 7 ΔL = −28.5 ΔE = 41.1 Δa =−7.0 Δb = −10.5 10 ΔL = −37.4 ΔE = 38.4 Δa = −4.5 Δb = −6.1

Example 5 Formulated Gel Compositions for Electrochemical ColoringSystem

This example illustrates formulated compositions for an electrochemicalcoloring system employing an electrically conducting gel structuringsystem. The compositions described in Table 4 were prepared and testedfor their effectiveness in electrochemical coloring. A combination ofCARBOPOL ETP 2020 (a Carbomer) and xanthan gum was employed for Example5 A while a combination of STRUCTURE XL and xanthan gum was used inExample 5 B. Both compositions were effective in the in-vitro coloringof Piedmont hair when a voltage of 3 to 6 volts was applied. Thesestructuring systems provided acceptable viscosity without interferingwith the electrochemical process. TABLE 4 Compositions for Example 5Example 5A Example 5B Ingredients Wt % Wt % Carbopol ETP 2020 0.75Structure XL 0.75 Xanthan Gum 0.10 0.10 Propylene Glycol 2.50 2.50Isopropanol 2.0 2.0 p-Amino-o-Cresol 0.35 0.35 p-Phenylenediamine 0.300.30 p-Aminophenol 0.10 0.10 Sodium perchlorate 0.50 0.50 Sodiumbisulfite 0.20 0.20 EDTA 0.10 0.10 Isoascorbic acid 0.10 0.10 Fragrance0.02 0.02 Sodium hydroxide 0.50 0.50 Water 92.48 92.48 Total 100.00100.00

Example 5 This Example Illustrates Electrochemical Hair Coloring Systems

-   A. Oxidative Dye precursor composition: Compositions of Example 5A    or 5B are packaged in separate containers-   B. Electrode System: Comb comprised of metal conducting tines    providing a 3 volt potential and delivering a current of 75 mA to    1.5 A. Power source: and AC to DC converter or a rechargeable    battery Ratio of anode to cathode surface area is 1.5.

Example 7 This Example Illustrates a Kit Comprising an AdditionalInstruction Sheet

The invention also relates to a kit for carrying out the electrochemicalhair coloring method of the invention. The kit may comprise a hair dyeprecursor part, an electrode system optionally coupled to an alignmentand distributing means, and a post treatment solution. Each componentmay be in a separate container or in a dual container, as describedherein. The kit may optionally comprise an integrated system thatincorporates two or more of the above means to carry out the above step,e.g., an electrode system that dispenses the dye precursor mixture. Thekit also contains written instructions that explain how the compositionsof the invention are used. For example, “Apply precursor mixture tohair. After 10 minutes, turn on the electrochemical color-developingcomb and comb the hair until the desired color is achieved. After 15minutes rinse hair well and dry”.

The consumer can admix the components of the kit according to writteninstructions, to obtain the aqueous reaction mixture. After treatmentfor a desired time with the hair dye precursor composition, theelectrode system of the kit is used to align the hair, distribute theprecursors and to develop the color. The excess dye may be removed,preferably with water or a conventional shampoo or a conventionalconditioning shampoo.

A variety of alternative electrode systems can be provided with the kitas described above. These can range from a simple disposable or reusablecomb or a brush, or a more elaborate mesh-like “bonnet” havingelectrodes contacting the hair.

Several types of kits can be provided. For example a starter kitcomprising a precursor mixture and a reusable electrode system as wellas individual kits comprising for example, refills, touch-up orstreaking mixtures.

Desired change in hair color by the method of the invention is describedby the mathematical formula described above. Desired change in haircolor can be achieved in a number of other ways. In the first instance,the consumer can initially compare his or her hair color with desiredhair color or the hair color of a sample tress. Hair dyeing by themethod of the invention can be repeated until his or her hair colormatches the desired hair color.

Desired hair color can also be reached by comparing hair after eachtreatment until it matches hair tresses taken from the consumer during aprior treatment.

Desired hair color can also be reached by testing the hair after eachtreatment with instruments, which measure the color of the hair. Whenthe measurements of hair color of the treated hair reach a desiredlevel, the treatment hair reach a desired level, the treatment can bestopped.

Indeed, reaching the desired hair color can be achieved by the use ofany matching or comparison method commonly employed in the art. Further,the electrode system can incorporate a variable voltage adjustmentfeature that allows the consumer to gradually color the hair or to“dial-in” shades, i.e., by adjusting the voltage according to a colorchart supplied with the kit.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention and all suchmodifications are intended to be included within the scope of thefollowing claims.

1. A method of electrochemically dyeing and highlighting hair comprisingthe steps of: i) applying to the hair an oxidative dye precursor mixturecontaining at least one primary intermediate having a standard Redoxpotential less than about 1 volt, and optionally, an oxidizing agent,ii) contacting the oxidative dye precursor mixture on the hair with anelectrode system that provides sufficient voltage to electrochemicallyoxidize at least one of the primary intermediates to produce a reactiveintermediate that generates colored dye through a coupling reaction withan oxidative dye precursor present in the mixture
 2. The methodaccording to claim 1 wherein the primary intermediate is selected fromthe group consisting of p-phenylenediamine, substitutedp-phenylenediamine, p-aminophenol, substituted p-aminophenol, an indole,a substituted indole and mixtures thereof.
 3. The method according toclaim 1 wherein the oxidative dye precursor further comprises a couplerselected from the group consisting of m-substituted phenols,aminophenols and diamines, their derivatives, and mixtures thereof. 4.The method according to claim 1 wherein the oxidative dye precursormixture has a pH in the range from about 5 to about
 10. 5. The methodaccording to claim 1 wherein the oxidative dye precursor mixture has apH in the range from about 7 to about
 10. 6. The method according toclaim 1 wherein the oxidative dye precursor mixture additionallycontains supporting electrolytes which are electrochemically inert saltsselected from the group consisting of perchlorates, sulfates, borates,and mixtures thereof.
 7. The method according to claim 1 wherein theoxidative dye precursor mixture is free of chemical oxidizing agentsand/or ammonia.
 8. The method according to claim 1 wherein the oxidativedye precursor mixture additionally comprises a shear thinningelectrically conducting gel.
 9. The method according to claim 1 whereinthe electrode system comprises a plurality of anodes in contact with theprecursor mixture on the hair and one or more cathodes, wherein thetotal surface area of the anodes is greater than the total surface areaof the cathodes.
 10. The method according to claim 1 wherein theelectrode system further comprises an aligning and distributing meanscomprising at least one comb element or at least one brush element or acombination of comb and brush elements.
 11. The method according toclaim 1 wherein the electrode system further comprises a cloth orplastic bonnet or cap into which electrodes are embedded that cancontact the hair to which the precursor mixture is applied.
 12. Themethod according to claim 1 wherein the voltage is provided by adisposable or rechargeable battery or an electrical storage device thatconverts mechanical energy to electricity or an AC to DC converter. 13.The method according to claim 1 wherein the electrode system furthercomprises a switch, an on-off indicator, a voltage or current regulator,and a delivery means for the precursor mixture or combinations thereof.14. The method according to claim 1 wherein the electrode systemprovides a regulatable voltage such that different colored dye moleculescan be produced from a single dye precursor mixture depending upon thevoltage selected.
 15. The method according to claim 1 wherein at least50% of the colored dye molecules that are formed are formedelectrochemically, and not by chemical oxidation from either a bleach oroxygen oresent in the air or generated electrochemically.
 16. A systemfor electrochemically dyeing or highlighting the hair comprising: i) anoxidative dye precursor mixture containing at least one primaryintermediate having a standard oxidation potential less than about 1Vand optionally, an oxidizing agent, iii) an electrode system thatprovides sufficient voltage to electrochemically oxidize at least one ofthe primary intermediates to produce a reactive intermediate thatgenerates colored dye molecules through a coupling reaction with anoxidative dye precursor present in the mixture
 17. The system accordingto claim 15 wherein the primary intermediate is selected from the groupconsisting of p-phenylenediamine, substituted p-phenylenediamine,p-aminophenol, substituted p-aminophenol, an indole, a substitutedindole and mixtures thereof.
 18. The system according to claim 15wherein the oxidative dye precursor mixture further comprises a couplerselected from the group consisting of m-substituted phenols,aminophenols and diamines, their derivatives, and mixtures thereof. 19.The system according to claim 15 wherein the oxidative dye precursormixture has a pH in the range from about 5 to about
 10. 20. The systemaccording to claim 15 wherein the oxidative dye precursor mixture has apH in the range from about 7 to about
 10. 21. The system according toclaim 15 wherein the oxidative dye precursor mixture additionallycontains salts selected from the group consisting of perchlorates,sulfates, borates, and mixtures thereof.
 22. The system according toclaim 15 wherein the oxidative dye precursor mixture is free of chemicaloxidizing agents and/or ammonia.
 23. The system according to claim 15wherein the electrode system comprises a plurality of anodes in contactwith the precursor mixture on the hair and one or more cathodes, whereinthe total surface area of the anodes is greater than the total surfacearea of the cathodes.
 24. The system according to claim 15 wherein theelectrode system is further comprised of an aligning and distributingmeans comprising at least one comb element or one brush element or acombination of comb and brush elements.
 25. The system according toclaim 15 wherein the electrode system further comprises a cloth orplastic bonnet or cap into which electrodes are embedded that cancontact the hair to which the precursor mixture is applied.
 26. Thesystem according to claim 15 wherein the voltage is provided by adisposable or rechargeable battery, a storage device that convertsmechanical energy to electricity or an AC to DC converter.
 27. Thesystem according to claim 15 wherein the electrode system furthercomprises a switch, an on-off indicator, a voltage or current regulator,and a delivery means for the precursor mixture or combinations thereof.28. The system according to claim 15 wherein the electrode systemprovides a regulatable voltage such that different colored dye moleculescan be produced from a single dye precursor mixture depending upon thevoltage selected.
 29. The system according to claim 15 additionallyincluding written instructions to first apply the oxidative dyeprecursor mixture to the hair, and after a period of time ranging fromabout 0.5 minutes to 45 min, apply the electrode system and allow it tocontact the hair for a period of time ranging from about 30 seconds toabout 30 minute or a sufficient time to develop highlights or a desiredcoloring effect.
 30. The method according to claim 1 wherein theoxidizing agent is hydrogen peroxide.
 31. The method according to claim16 wherein the oxidizing agent is hydrogen peroxide.